Résumé :
|
Antisense-mediated reading frame restoration is one of the most promising therapeutic approaches for Duchenne muscular dystrophy (DMD). It uses antisense oligonucleotides (AONs) to induce exon skipping during pre-mRNA splicing of mutated dystrophin transcripts. This is aimed to restore the disrupted open reading frame and allow synthesis of internally deleted, partly functional Becker-like dystrophin proteins. Proof of concept has been obtained in cultured cells and the mdx mouse model and this approach is currently tested in clinical trials by Prosensa/GSK (GSK2402968 and PRO044) and AVI Biopharma (AVI-4658).Dystrophic animal models allow detailed analysis of pharmacokinetic and pharmacodynamic effects of AONs. The 2'-O-methyl phosphorothioate (2OMePS) chemistry used in the Prosensa/GSK trials and in our experiments has favorable pharmacokinetic properties: the PS backbone binds serum proteins, which prevents clearance by the kidney and increases serum half life. Uptake by healthy muscle is low, but we have previously shown that after systemic delivery of 2OMePS AONs, the AON levels in dystrophic skeletal muscle are up to 10-fold higher, and that subcutaneous delivery of 2OMePS is possible. Here, we optimized dosing and maintenance regimes using subcutaneous 2OMePS AON injections in the mdx mouse model. In addition, we tested the safety and efficacy of high dose (200 mg/kg/week) AON treatment for up to 6 months in mouse models with varying levels of severity: mdx mice (mild phenotype) and mdx mice with one utrophin allele (mdx +/-; intermediate phenotype). This was well tolerated during treatment and liver and kidney weights and serum parameters were similar treated mice compared to saline treated controls at the end of treatment. Notably, in the more severely affected mdx +/- mice the therapeutic effect was larger: exon skip and dystrophin levels were higher, the creatine kinase levels were more decreased and rotarod running time was more increased. Preliminary results suggest that AON levels in the muscles of the more severely dystrophic mdx +/- are higher than in those in mdx mice, confirming the hypothesis that AON uptake is aided by the disease pathology.These results indicate that long term subcutaneous treatment with 2OMePS AONs is safe and efficient in dystrophic mouse models, which is encouraging for long term trials in patients, recently initiated by Prosensa Therapeutics/GSK.
|